The invention relates to a forging press of underfloor design having a travelling frame, which press comprises a stationary crosshead or platen and a travelling frame formed by an upper and lower travelling crosshead and columns connecting these.
At least one hydraulic piston-cylinder unit for effecting the working stroke is provided acting between the platen and the lower travelling crosshead, while at least one additional piston-cylinder unit for the retraction of the travelling frame is disposed to act between the platen and the upper travelling crosshead. In order to relieve the columns of forging presses of this type from the bending stresses caused by eccentric forging resistance, it is known to provide the underside of the platen with a guide shaft on which the lower travelling crosshead is guided, the guides in the lower travelling crosshead diverting the moment due to the eccentric forging resistance to the guide shaft (Ernst Muller "Hydraulische Pressen und Druckflussigkeitsanlagen" [Hydraulic Presses and Pressure Fluid Plants], Vol. 1 "Schmiedepressen" [Forging Presses], 3rd edition, Springer-Verlag, 1962, pp. 33, 34, FIG. 29). On account of the central arrangement of the guide shaft, two working-stroke piston-cylinder units are necessary at both sides of the guide shaft, since a greater than usual structural height would be produced if only one piston-cylinder unit were arranged centrally, coaxially, and thus as an extension of the guide shaft. In addition, a relatively substantial distance is necessary in the lower travelling crosshead between the guide sleeves that divert the moment to the guide shaft. These demands result in a considerable structural cost.
These disadvantages have been countered by constructing the guide shaft as a plunger piston and the lower travelling crosshead as a cylinder crosshead (Journal "MPT, Metallurgical Plant and Technology", Vol. 2, 1979, pp. 5 to 14, FIG. 3). Since this no longer has the exclusive guide on the guide sleeve (plunger piston), in addition to the guidance of the travelling crosshead by means of the cylinder on the guide shaft (constructed as a plunger piston) a further guide at a distance from the first guide is necessary, for which purpose the columns connecting the upper and lower travelling crosshead are guided in the platen. In this connection the guidance of the lower travelling crosshead by means of the cylinder on the plunger piston forming the guide shaft has been found to be disadvantageous, since the bottom bush and stuffing box, which form the guide means, in the cylinder are subjected to considerable transverse forces and therefore undergo considerable wear. The inevitable abrasion of the bottom bush and stuffing box caused by the wear can cause damage to pumps and control means by way of the operating medium. A further disadvantage which should be mentioned is that the centering bore required for securing the plunger piston in the platen weakens the platen or necessitates a special reinforcement of the platen.